Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$6.43	10.531%	$7.1071	$7.11	$7.10	$7.10
Purchase #2	$95.41	8.497%	$103.517	$103.52	$103.50	$103.50
Purchase #3	$247.81	3.608%	$256.751	$256.75	$256.75	$256.80
Purchase #4	$153.50	6.118%	$162.8911	$162.89	$162.90	$162.90
Purchase #5	$98.80	4.830%	$103.572	$103.57	$103.55	$103.60
Purchase #6	$19.66	11.659%	$21.9522	$21.95	$21.95	$22.00
Purchase #7	$11.73	13.763%	$13.3444	$13.34	$13.35	$13.30
7 purchase totals =	$633.34		$669.1348	$669.13	$669.10	$669.20